1. Field of the Invention
The present invention relates to wound dressings and methods for making same, and in particular to a wound dressing which can be applied to a patient without stretching thereof, and a method for the continuous production of a large number of such wound dressings.
2. Description of the Prior Art
Wound dressings consisting of thin flexible material, such as urethane, having adhesive on one side, which are applied to an open wound of a patient after medical treatment of the wound are known in the art. The flexible nature of the urethane permits the dressing to conform to virtually any contour of the patient at the location where the dressing is applied. The flexibility and thinness of the wound dressing, however, present the problem of applying the dressing to the patient without stretching the dressing. Stretching of the dressing prior to or during application thereof to a patient will momentarily expand the stretchable urethane, and even though the dressing may appear smooth when applied to the patient, the urethane will very quickly thereafter contract after the stretching forces are relieved, thereby causing discomfort to the patient and irritation to the area surrounding the wound. On weak or damaged skin, as in the elderly, the stretching forces can cause serious skin damage, such as an abcess. One proposed solution to the stretching problem was to use heavier polyurethane materials. These heavier materials are not desirable as a wound dressing due to decreased flexibility and less gas permeability.
Another proposed solution to this problem is to provide a flexible but non-stretching backing for the urethane wound dressing which remains in contact with the wound dressing by adhesive while the dressing is being applied to the patient, and is separated from the wound dressing only after the dressing has been placed on the patient, thereby eliminating stretching during application of the dressing. Such a wound dressing is described, for example, in European patent EP 0 066 899 A2. The wound dressing disclosed therein is a film sheet of polyurethane having adhesive on one side thereof which is applied to a patient. A non-stretchable film sheet carrier is pressed against the opposite side of the film sheet. The carrier may be bound to the film sheet either by the adhesion resulting from the urethane film sheet casting process, on a non-stretchable film sheet carrier or by a heat-dependent process to the non-stretchable carrier. A combination polyurethane film and MYLAR.RTM. polyester film (E.I. du Pont de Nemours, Wilmington, Del.) are commercially available. To this combination is added a free film of adhesive with the top adhesive backing left on the urethane film MYLAR.RTM. polyester film. Adhesive backing is peeled away prior to application to a patient. After the adhesive side of the film sheet is brought into contact with a patient, the Mylar.RTM. is peeled from the other side of the film sheet leaving polyurethane on the wound.
Another problem encountered when applying the polyurethane film to the wound is maintaining the sterility of the dressing during the application process. Previous products such as the polyurethane film wound dressings Ensure-It (Deseret Medical, Inc.) and Polyskin.RTM. transparent dressing (Kendall Company, Boston, Mass.) required contact between fingers and the adhesive surface of the polyurethane film during application, thereby potentially contaminating the adhesive surface adjacent to the wound beneath the polyurethane.
Still another problem is the presence of a tab or tabs remaining on the polyurethane film after application to the wound surface. The presence of a tab often results in a gradual loosening of the polyurethane film to skin adhesive bond resulting in a curling-up of the polyurethane film edge adjacent to the tab.
One solution to this tab problem required a perforation adjacent to the tabs, thereby allowing removal of the tabs after application of the polyurethane film to the skin surface. However, the act of tearing of the tab perforations disturbs the adhesive bond, distorts or stretches the polyurethane film and microbially contaminates the adhesive, thereby resulting in a less secure, less sterile and less comfortable wound dressing.
There has been a long felt need for a polyurethane film product that provides ease of application, maintains sterility and does not require distortion of the film sheet by tearing operations. The tab systems of the present invention meet this need.
Alvarez et al., Infections in Surgery, p. 173, Mar. 1, 1984, presented evidence that a completely occlusive dressing such as hydrocolloid, best promoted the healing rate of wounds up to 96 hours. After longer periods of time, 96 hours or longer, a gas permeable polyurethane film resulted in superior healing rates as measured by collagen synthesis. These results suggest that for some applications the ideal wound dressing would function as a completely occlusive dressing for a first period of time, then function as a semi-occlusive dressing for a second period of time.
The layered construction of wound coverings containing gas permeable polymers has long experienced a problem in manufacturing. The casting of a polymer film sheet, such as polyurethane, on a casting sheet resulted in a weak electrostatic bond (corona coating) between the liner and polymer film sheet. This weak bond was weakly effective at holding the film sheet to the liner. If this liner was used as a cover sheet it was not-replaceable once removed. Wound coverings were limited to the types of liners that could be used as casting sheets for the polymer; such use requires resistance to casting heat. The most common liner being MYLAR.RTM. polyester film, a relatively stiff material not possessing the flexible properties desired in a material suitable for the application as a flexible wound cover contouring agent. A need existed for a production method allowing the insertion of adhesive and the substitution of a more flexible cover sheet.